Gyroscope Shock and Disturbance Detection Circuit

ABSTRACT

The invention relates to integrated circuits, and more particularly, to systems, devices and methods of integrating a gyro sensing circuit with a gyroscope to detect a shock or a disturbance, and accurately differentiate rotation-based sense signals from noises introduced by the shock or disturbance. The gyro sensing circuit may be implemented in a differential or non-differential demodulation scheme, and comprises at least one demodulation unit and a peak detector. The at least one demodulation unit demodulates a gyro output signal provided by the gyroscope with a reference signal. In a demodulated gyro output signal, a shock signal or a gyro disturbance signal is substantially isolated out from interested gyro sense signals that are used to sense a rate of rotation. A peak detector samples the modulated gyro output signal, determines whether the signal exceeds a threshold level V TH  and outputs a shock flag indicating a corresponding determination result.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of previously filed and copendingapplication Ser. No. 13/925,741, entitled, “Gyroscope Shock andDisturbance Detection Circuit, naming Massimiliano Forliti and ChristianRosadini as inventors, and filed Jun. 24, 2013, which application claimsthe benefit under 35 U.S.C. §119(e) of Provisional Application No.61/816,419, entitled “Gyroscope Shock and Disturbance DetectionCircuit,” filed Apr. 26, 2013, which applications are herebyincorporated herein by reference in their entireties.

BACKGROUND

A. Technical Field

The present invention relates to integrated circuits, and moreparticularly, to systems, devices and methods of detecting a shock or adisturbance experienced by a gyroscope and differentiatingrotation-based sense signals from noises introduced by the shock ordisturbance.

B. Background of the Invention

A microelectromechanical structure (MEMS) is widely applied as a sensorto measure acceleration, rotation, pressure and many other physicalparameters. The MEMS device is normally formed on a silicon substrateusing a micromachining process, adopts characteristic feature sizes ofseveral micrometers, and transduces mechanical movement to electricalsignals that may indicate the level of an interested parameter. Inparticular, MEMS-based gyroscope devices have been developed and appliedto monitor rotational rates of the devices with respect to certain axes,and a multitude of consumer and automotive applications havesuccessfully adopted such MEMS-based gyroscope devices. For instance,many automotive integrate the gyroscope devices for vehicle stabilitycontrol, navigation assist, load leveling/suspension control, collisionavoidance and roll over detection.

Conventional MEMS-based gyroscope devices use vibrational mechanicalelements (proof masses) to sense a rate of rotation. FIG. 1A illustratesa mechanical element 100 disposed in a rotating reference frame. Themechanical element 100 is driven to oscillate in a first orthogonal axis(x-axis), and as the frame rotates with respect to a second orthogonalaxis (y-axis), vibratory movement is induced along the third orthogonalaxis (z-axis) due to Coriolis acceleration. A corresponding inertialCoriolis force F_(C) may be represented as:

F _(C)=−2Ωmv  (1)

where Ω is the rate of rotation, m is the mass of the mechanical element100 and v is the vibrational velocity along the first orthogonal axis.

FIG. 1B illustrates an exemplary vibratory gyroscope device 150 thatrelies on electrostatic actuation and capacitive sensing to detect theCoriolis force. A proof mass 152 is driven to vibrate along an x-axis bycomb drivers 154 arranged at two opposing sides. A capacitor is formedbetween the substrate and the proof mass 152. In response to rotationwith respect to a y-axis, the proof mass 152 vibrates towards and awayfrom a substrate that the gyroscope device 150 is situated on, andtherefore, the gap distance of the capacitor varies, leading to acapacitive variation that is associated with the Coriolis force. Aninterface readout circuit is normally integrated with the gyroscopedevice 150 to convert this capacitive variation to a gyroscope sensesignal that is related to the magnitude of the Coriolis force andtherefore to the corresponding rate of rotation.

Although the gyroscope sense signal includes interested informationrelated to the rate of rotation, noises are also introduced by variousshock and disturbance sources and could significantly compromise theaccuracy of rotation sensing. Particularly in automotive applications,shock robustness is critical and constitutes a key characteristic,because strict safety constraints have to be imposed to ensure afailsafe and robust system. In such a context, an occurrence of shock ordisturbance needs to be flagged and used to indicate that an unreliableand unpredictable rate signal is outputted, when the level of the shockor disturbance exceeds a threshold value tolerable by a correspondingrotation sensing system. Many existing gyroscope devices in the markethave adopted sensor or package solutions to improve shock robustness ofthe devices themselves. However, none of them flags the occurrence ofshock or disturbance with respect to a certain tolerance, and warns ahost to take suitable countermeasures.

SUMMARY OF THE INVENTION

Various embodiments of the invention relate to integrated circuits, andmore particularly, to systems, devices and methods of integrating a gyrosensing circuit with a gyroscope to detect a shock or a disturbanceexperienced by a gyroscope device and accurately differentiaterotation-based gyro sense signals from noises introduced by the shock ordisturbance. The gyro sensing circuit specifically takes advantages ofthe symmetry of these signals with respect to a characteristic frequencyof the gyroscope.

In accordance with one embodiment of the invention, a gyro sensingcircuit is implemented based on a differential demodulation scheme. Twodemodulate units are applied to demodulate a gyro output signal thatcomprises a shock signal and a plurality of gyro sense signals. Tworeference signals that are symmetric with respect to the characteristicfrequency are used for the demodulation, and the resulting demodulatedgyro outputs are differentially combined in a subtractor to isolate theshock signal that is asymmetric with respect to the characteristicfrequency. A peak detector further determines whether the combined gyrooutput exceeds a threshold level, and generates a shock flag to alert ahost whether an anomalous shock or disturbance situation occurs.

In accordance with another embodiment of the invention, a gyro sensingcircuit is implemented based on a non-differential demodulation scheme.The gyro sensing circuit comprises a demodulation unit and a peakdetector. The demodulation unit is first coupled to receive a gyrooutput signal that comprises a gyro sense signal and at least one of ashock signal and a plurality of gyro disturbance signals from agyroscope. Such a gyro output signal is demodulated using a referencesignal, such that the at least one of the shock signal and the pluralityof gyro disturbance signals is retained while the gyro sense signal thatis related to an interested rate of rotation is suppressed. The peakdetector determines whether the demodulated gyro output exceeds athreshold level and generates a shock flag to alert a host whether ananomalous shock or disturbance situation occurs.

Certain features and advantages of the present invention have beengenerally described here; however, additional features, advantages, andembodiments are presented herein will be apparent to one of ordinaryskill in the art in view of the drawings, specification, and claimshereof. Accordingly, it should be understood that the scope of theinvention is not limited by the particular embodiments disclosed in thissummary section.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to embodiments of the invention, examples ofwhich may be illustrated in the accompanying figures. These figures areintended to be illustrative, not limiting. Although the invention isgenerally described in the context of these embodiments, it should beunderstood that it is not intended to limit the scope of the inventionto these particular embodiments.

FIG. 1A illustrates a mechanical element disposed in a rotatingreference frame.

FIG. 1B illustrates an exemplary vibratory gyroscope device that relieson electrostatic actuation and capacitive sensing to detect a Coriolisforce.

FIG. 2 illustrates an exemplary rotation sensing system according tovarious embodiments in the invention.

FIG. 3 illustrates an exemplary block diagram of a gyro sensing circuitbased on a non-differential demodulation scheme according to variousembodiments in the invention.

FIG. 4A illustrates a first exemplary spectrum diagram of inputs coupledinto a rotation sensing system according to various embodiments in theinvention.

FIG. 4B illustrates a first exemplary spectrum diagram of signalcomponents in a gyro output signal and a reference signal used in a gyrosensing circuit according to various embodiments in the invention.

FIG. 4C illustrates an exemplary spectrum diagram that indicates amechanism to separate a shock signal from two gyro sense signals in agyro output signal according to various embodiments in the invention.

FIG. 5A illustrates a second exemplary spectrum diagram of inputscoupled into a rotation sensing system according to various embodimentsin the invention.

FIG. 5B illustrates a second exemplary spectrum diagram of signalcomponents in a gyro output signal and a reference signal used in a gyrosensing circuit according to various embodiments in the invention.

FIG. 5C illustrates an exemplary spectrum diagram that indicates amechanism to separate one of two gyro disturbance signals from the twogyro sense signals in a gyro output signal according to variousembodiments in the invention.

FIG. 6 illustrates an exemplary block diagram of a gyro sensing circuitbased on a differential demodulation scheme according to variousembodiments in the invention.

FIG. 7A illustrates a third exemplary spectrum diagram of inputs coupledinto a rotation sensing system according to various embodiments in theinvention.

FIG. 7B illustrates an exemplary spectrum diagram of signal componentsin a gyro output signal and two reference signals used in a gyro sensingcircuit according to various embodiments in the invention.

FIG. 7C illustrates an exemplary spectrum diagram that indicates adifferential demodulation mechanism to separate a shock signal from gyrosense and disturbance signals a gyro output signal according to variousembodiments in the invention.

FIG. 8 illustrates another exemplary block diagram of a gyro sensingcircuit based on a differential demodulation scheme according to variousembodiments in the invention.

FIG. 9A illustrates an exemplary flow diagram of a method for flagging adisturbance or a shock experienced by a rotation sensing systemaccording to various embodiments in the invention.

FIG. 9B illustrates another exemplary flow diagram of a method forflagging a shock experienced by a rotation sensing system according tovarious embodiments in the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for the purpose of explanation, specificdetails are set forth in order to provide an understanding of theinvention. It will be apparent, however, to one skilled in the art thatthe invention can be practiced without these details. One skilled in theart will recognize that embodiments of the present invention, describedbelow, may be performed in a variety of ways and using a variety ofmeans. Those skilled in the art will also recognize additionalmodifications, applications, and embodiments are within the scopethereof, as are additional fields in which the invention may provideutility. Accordingly, the embodiments described below are illustrativeof specific embodiments of the invention and are meant to avoidobscuring the invention.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, characteristic, or functiondescribed in connection with the embodiment is included in at least oneembodiment of the invention. The appearance of the phrase “in oneembodiment,” “in an embodiment,” or the like in various places in thespecification are not necessarily all referring to the same embodiment.

Furthermore, connections between components or between method steps inthe figures are not restricted to connections that are effecteddirectly. Instead, connections illustrated in the figures betweencomponents or method steps may be modified or otherwise changed throughthe addition thereto of intermediary components or method steps, withoutdeparting from the teachings of the present invention.

Various embodiments of the invention relate to integrated circuits, andmore particularly, to systems, devices and methods of integrating a gyrosensing circuit with a gyroscope to detect a shock or a disturbanceexperienced by a gyroscope device and accurately differentiaterotation-based gyro sense signals from noises introduced by the shock ordisturbance. In addition to the rotation-based gyro sense signals, gyrodisturbance signals or a shock signal may be incorporated in a gyrooutput signal provided by the gyroscope device to the gyro sensingcircuit, but these signals have different frequency magnitudes andcharacteristics. When the shock signal exceeds a threshold level, thegyro output signal is corrupted, and a rate of rotation derived from thegyro output signal is not reliable any more. Sometimes, the gyro outputsignal is also regarded as corrupted when one of the gyro disturbancesignals exceeds the threshold level.

In accordance with the invention, the gyro sensing circuit is configuredaccording to a differential or non-differential demodulation scheme, andapplies at least one reference signal to demodulate the gyro outputsignal. The reference frequency of the at least one reference signal isselected according to the frequencies of the shock signal or the gyrodisturbance signals, such that the shock or disturbance signals may beseparated from the rotation-based gyro sense signals in the gyro outputsignal. The shock or disturbance signals are constantly monitored, andany anomalous situation is flagged out to a host that relies on thegyroscope for rotation sensing. Upon detection of such conditions, thehost may take suitable countermeasures, such as ignoring the corruptedgyro output signal, to ensure the accuracy of rotation sensing.

FIG. 2 illustrates an exemplary rotation sensing system 200 according tovarious embodiments in the invention. The rotation sensing system 200comprises a gyroscope device 202 and a gyro interface circuit 204 thatfurther comprises a driver circuit 206 and a gyro sensing circuit 208.In accordance with various embodiments of the invention, the gyroscopedevice 202 is a MEMS device manufactured from a micro-fabricationprocess. The driver circuit 206 provides a drive signal toelectrostatically drive a proof mass included in the gyroscope device202, and the proof mass is therefore driven to oscillate along a firstorthogonal direction in a rotating reference frame. The drive signalpreferably has a drive frequency that is consistent with acharacteristic frequency f₀ of the gyroscope device 202. In response torotation with respect to a second orthogonal direction, the proof massoversees a physical displacement along a third orthogonal direction anda corresponding capacitive variation. The gyro sensing circuit 208 iscoupled to sense the capacitive variation which is associated with acorresponding Coriolis force along the third orthogonal direction.

The gyroscope 202 provides a gyro output signal to the gyro sensingcircuit 204, and this gyro output signal contains gyro sense signalsresulting from an interested rotation rate of the gyroscope 202. In apreferred embodiment, the gyro output signal is only associated with thecapacitive variation caused by the Coriolis force, and contains only thegyro sense signals. However, in many cases, a shock or disturbance maybe incorporated and unavoidably impact the gyro output signal.Therefore, the gyro output signal oftentimes includes a shock signal orgyro disturbance signals induced by the shock or disturbance,respectively.

In accordance with the present invention, the gyro sensing circuit 208detects and flags an undesirable shock or disturbance in addition torotation sensing, when a certain shock or disturbance signal containedin the gyro output signal exceeds a threshold level. Under suchcircumstances, useful information concerning a rate of rotationassociated with the gyro output signal is corrupted by the excessiveshock or disturbance signal and rendered inaccurate. Accordingly, anapplication host that adopts the rotation sensing system 200 may rely ona shock flag generated by the gyro sensing circuit 208 to determinewhether the gyro output signal needs to be ignored and dissociated fromthe interested rate of rotation.

The mechanical structure of the gyroscope device 202 may be abstractlyrepresented in theory as a combination of a mixer 202A and a low-passfilter 202B. The mixer 202A mixes the drive signal and the rate ofrotation, and generates an intermediate gyro output signal that isassociated with the corresponding Coriolis force. The intermediate gyrooutput signal is further filtered to generate the gyro output signal.The low-pass filter 202B is associated with a transfer function H_(p)(s)that has a resonance peak at a peak frequency f₁. The cut-off frequencyof the low-pass filter 202B is substantially consistent with the peakfrequency f₁. The characteristic frequency f₀ of the gyroscope device202 is smaller than the peak frequency f₁, and thus, the gyro outputsignal may accurately maintain the interested information related to therate of rotation. In one specific embodiment, the characteristicfrequency f₀ and the peak frequency f₁ are respectively 20 kHz and 21kHz.

An analog filter 210 may be further disposed at an input of the gyrosensing circuit 208. The analog filter 210 is a low-pass filter used tofilter, scale or amplify the gyro output signal prior to any furtherprocessing. The analog filter 210 serves anti-aliasing purposes, anddoes not affect the rotation-related spectrum content of the gyro outputsignal. Therefore, the cut-off frequency of the analog filter 210 isselected to be larger than both the characteristic frequency f₀ and thepeak frequency f₁. For example, the cut-off frequency of the analogfilter 210 may be set as 100 kHz, when the characteristic frequency f₀and the peak frequency f₁ of the gyroscope 202 are respectively 20 kHzand 21 kHz.

In some embodiments, the gyro output signal provided by the gyroscope202 is an analog signal. Upon filtering and scaling/amplification withinthe analog filter 210, the gyro output signal is converted to a digitalsignal that may be further processed in a digital domain to obtain therate of rotation and generate the flag output.

In certain embodiments, the gyroscope device 202 and the gyro interfacecircuit 204 are manufactured on two separate substrates, and assembledto form the rotation sensing system 200 in a hybrid format. In someother embodiments, the gyroscope device 202 and the gyro interfacecircuit 204 are manufactured on one single substrate using amicro-fabrication process that involves multiple layers of material.Even though they may occupy distinct chip estates that are physicallyseparated on the substrate, the gyroscope device 202 may also beintegrated on top of the gyro interface circuit 204 to save the chipestate. For such a vertical integration, the manufacturing process, thematerial layers and the configurations of both the gyroscope device 202and the interface circuit 204 have to be properly arranged.

FIG. 3 illustrates an exemplary block diagram 300 of a gyro sensingcircuit based on a non-differential demodulation scheme according tovarious embodiments in the invention. The gyro sensing circuit 300generates a shock flag that indicates whether a shock or disturbancesignal exceeds a threshold level V_(TH), and therefore, the applicationhost may rely on the shock flag to determine whether the gyro outputsignal is corrupted and needs to be ignored.

The gyro sensing circuit 300 comprises a demodulation unit 302 and apeak detector 304. The demodulation unit 302 demodulates a gyro outputsignal using a reference signal, such that the shock or disturbancesignal is retained while the gyro sense signals are suppressed within ademodulated gyro output signal. By this means, the shock or disturbancesignal is effectively separated out from the gyro sense signals. Thepeak detector 304 further detects whether the magnitude of thedemodulated gyro output signal exceeds a threshold level V_(TH), andgenerates the corresponding shock flag to alert the host whether ananomalous shock or disturbance situation occurs.

The demodulation unit 302 further comprises an electronic mixer 306 anda low-pass filter 308. The electronic mixer 306 combines the referencesignal and the gyro output signal, and varies the spectrum contents ofthe gyro output signal with respect to a reference frequency f_(R) ofthe reference signal. The low-pass filter 308 adopts a gain G_(LP) and acut-off frequency f_(LP) that are designed to differently process theshock or disturbance signal and the gyro sense signals in the gyrooutput signal, and in particular, to retain or amplify the level of theshock or disturbance signal while suppressing that of the gyro sensesignals. A selection method is applied to determine the referencefrequency f_(R), the cut-off frequency f_(LP) and the gain G_(LP), and acorresponding rationale underneath such a selection method is detailedbelow in FIGS. 4A-4C and FIGS. 5A-5C.

The peak detector 304 comprises a sampling circuit 310 and a comparator312. The sampling circuit 310 samples the demodulated gyro output signalreceived from the demodulation unit 302. The comparator 312 compares thesampled signal with the threshold level V_(TH) and generates the shockflag according to a comparison result.

FIG. 4A illustrates a first exemplary spectrum diagram 420 of inputscoupled into a rotation sensing system according to various embodimentsin the invention. Rotation of the gyroscope device 202 is incorporatedvia the capacitive variation associated with the Coriolis force, andnormally has a relatively low rotation frequency Ω. Such a rotation isdirectly associated with vehicle motion, when the host is a vehicle, andrepresents a useful signal that a supplier or a user of a host isinterested in. The rate of rotation is normally located at a lower endof the frequency spectrum. In some embodiments, the rotation frequency Ωmay be limited below 300 Hz.

A mechanical shock is normally introduced to the rotation sensing system200 by acceleration stimuli or generic vibrations that are experiencedby the host. The shock is directly incorporated into the gyro outputsignal without mechanical modulation by the gyroscope device 202.Therefore, a shock frequency f_(SK) associated with the shock is notlimited by the low-pass filter 202B, and in certain embodiments, may behigher than the characteristic frequency f₀ or the peak frequency f₁ ofthe gyroscope 202. In one embodiment, the shock frequency f_(SK)approximately extends up to 30 kHz, when the characteristic frequency f₀and the peak frequency f₁ of the gyroscope 202 are respectively 20 kHzand 21 kHz.

FIG. 4B illustrates a first exemplary spectrum diagram 440 of signalcomponents in a gyro output signal and a reference signal used in a gyrosensing circuit according to various embodiments in the invention. Basedon equation (1), the rotation of the gyroscope 202 is modulated to twogyro sense signals that are symmetric around the characteristicfrequency f₀. Two sense frequencies of these two gyro sense signals arerespectively f₀−Ω and f₀+Ω, and in certain embodiments, the sensefrequencies may range from DC to 15 kHz. On the other hand, the shocksignal is not modulated by the gyroscope 202, and directly incorporatedinto the gyro output signal. The first gyro sense signal, the secondgyro sense signal and the shock signal constitute the signal componentsof the gyro output signal received from the gyroscope 202.

In view of the signal components, the reference frequency f_(R) of thereference signal is particularly selected to be closer to the shockfrequency f_(SK) than to either of the two gyro sense frequencies f₀−Ωand f₀+Ω. On one hand, the reference frequency f_(R) also needs to besufficiently far from the peak frequency f₁ of the gyroscope 202. Thisis particularly due to the fact the peak frequency f₁ is associated withan intrinsic vibrational mode of the gyroscope 202 and that a spuriousamplified response may be undesirably produced around this peakfrequency f₁. On the other hand, the reference frequency f_(R) is not sofar from the shock frequency that a response from the shock signal couldbe compromised as well

In certain embodiments, the shock signal is not limited to one singlefrequency, and the shock frequency f_(SK) is associated with a bandwidthBW_(SK). The reference frequency f_(R) is still similarly determined asabove, but particularly selected to be close to or within the frequencyspan of the shock frequency f_(SK).

FIG. 4C illustrates an exemplary spectrum diagram 460 that indicates amechanism to separate the shock signal from the two gyro sense signalsaccording to various embodiments in the invention. The shock signal andthe two gyro sense signals are converted with respect to the referencesignal, and change to different frequencies from their originalfrequencies in the electronic mixer 306. The characteristic frequency f₀is converted to a demodulated characteristic frequency |f_(R)−f₀|.Likewise, the modulated frequencies of the shock signal and the two gyrosense signals are |f_(R)−f_(SK)|, |f_(R)−(f₀.Ω)| and |f_(R)−(f₀+Ω)|,respectively. The absolute values are applied, because in someembodiments, the reference frequency f_(R) is smaller than the shockfrequency f_(SK) or the gyro sense frequency f₀−Ω.

In this embodiment, the reference frequency f_(R) is larger than boththe shock frequency f_(SK) and the gyro sense frequencies f₀−Ω and f₀+Ω.The modulated frequencies of the shock signal and the two gyro sensesignals may be simply represented as f_(R)−f_(SK), f_(R)−(f₀.Ω) andf_(R)−(f₀+Ω), respectively

The cut-off frequency f_(LP) of the low-pass filter 308 is controlledbetween the modulated shock frequency |f_(R)−f_(SK)| and the modulatedgyro sense frequencies, i.e., |f_(R)−(f₀.Ω)| and |f_(R)−(f₀+Ω)|. Thelevel of the shock signal is retained or amplified by the gain G_(LP).On the opposite, the first and second gyro sense signals are depressed.Upon such modulations based on mixing and low pass filtering, the shocksignal in the gyro output signal is separated, and the peak detector 304may further determine whether the shock signal exceeds the thresholdlevel V_(TH).

One of those skilled in the art knows that the gyro sensing circuit 300is preferably applied when the shock signal is not modulated by thegyroscope device 202 and relatively distant from the gyro sense signalson the frequency spectrum. The difference between the shock frequencyf_(SK) and the sense frequencies f₀±Ω needs to be sufficiently large,such that the cut-off frequency f_(LP) may be controlled to a magnitudein between of them.

The modulation method based on one demodulation unit 302 is notapplicable when the shock frequency f_(SK) is substantially close toeither of the sense frequencies f₀−Ω and f₀+Ω in FIG. 4C. Substantialcloseness of the shock frequency with another frequency is determinedbased on whether the cut-off frequency f_(LP) of the low-pass filter 308may be engineered to differentiate the corresponding modulatedfrequencies. To be specific, in one embodiment associated with FIG. 4C,a challenge occurs for the gyro sensing circuit 300 that is based on asingle modulation unit 302, when the modulated shock frequencyf_(R)−f_(SK) and the modulated gyro sense frequency f_(R)−f₀−Ω is soclose that the low-pass filter 308 may not be easily engineered todifferentiate them.

However, in some embodiments, the gyroscope 202 may further couplerotational disturbance besides the interested rotation of the host. Whenthe host is a vehicle, such rotational disturbance may result frominternal vehicle vibration or parasitic vibration of a gyroscopepackage. In particular, the rotational disturbance is modulated by thegyroscope 202 to generate gyro disturbance signals that have symmetricdisturbance frequencies with respect to the characteristic frequency f₀.

FIG. 5A illustrates a second exemplary spectrum diagram 520 of inputscoupled into a rotation sensing system according to various embodimentsin the invention. In addition to interested rotation, a rotationaldisturbance to the gyroscope device 202 is also incorporated via thecapacitive variation associated with the Coriolis force. Such arotational disturbance has a disturbance frequency f_(RD) that isnormally located within an intermediate frequency range, e.g., 1-5 kHz.In many embodiments, the disturbance frequency f_(RD) is smaller thanthe characteristic frequency f₀ of the gyroscope 202.

FIG. 5B illustrates a second exemplary spectrum diagram 540 of signalcomponents in a gyro output signal and a reference signal used in a gyrosensing circuit according to various embodiments in the invention.Similarly, the rotational disturbance of the gyroscope 202 is modulatedto two gyro disturbance signals that are symmetric with respect to thecharacteristic frequency f₀. Two gyro disturbance frequencies of thesetwo gyro disturbance signals are respectively f₀−f_(DR) and f₀+f_(DR).These two gyro disturbance signals and the two gyro sense signalsconstitute the signal components in the gyro output signal received fromthe gyroscope 202. The gyro disturbance signals are further apart fromthe characteristic frequency f₀ compared with the gyro sense signals,because the rotational disturbance normally has a higher frequency thanthat of the interested rotation itself.

In view of these signal components, the reference frequency f_(R) of thereference signal is particularly selected to be closer to either of thetwo gyro disturbance frequencies f₀−f_(DR) and f₀+f_(DR) than to bothgyro sense frequencies f₀−Ω and f₀+Ω. To be specific, the referencefrequency f_(R) may be selected to be smaller than the characteristicfrequency f₀, and therefore, closer to the gyro disturbance frequencyf₀−f_(DR) than to the gyro sense frequency f₀−Ω. Otherwise, thereference frequency f_(R) may be selected to be larger than thecharacteristic frequency f₀, and therefore, closer to the gyrodisturbance frequency f₀+f_(DR) than to the gyro sense frequency f₀+Ω.

Nevertheless, the reference frequency f_(R) needs to be sufficiently farfrom the peak frequency f₁ of the gyroscope 202 to avoid undesirableamplification that is associated with the intrinsic vibrational mode ofthe gyroscope at this peak frequency. On the other hand, this referencefrequency f_(R) is not so far from one of the gyro disturbancefrequencies that a response from the disturbance signal could becompromised.

FIG. 5C illustrates an exemplary spectrum diagram 560 that indicates amechanism to separate one of the two gyro disturbance signals from thetwo gyro sense signals according to various embodiments in theinvention. The two gyro disturbance signals and the two gyro sensesignals are converted with respect to the reference signal f_(R), andchange to different frequencies from their original frequencies in theelectronic mixer 306. As a result, the modulated frequencies of the twogyro disturbance signals are |f_(R)−(f₀.f_(RD))| and|f_(R)−(f₀+f_(RD))|, respectively, while the modulated frequencies ofthe two gyro sense signals are |f_(R)−(f₀−Ω)| and |f_(R)−(f₀+Ω)|,respectively. The absolute values are applied, because in someembodiments, the reference frequency f_(R) is smaller than either of thegyro disturbance frequencies f₀±f_(RD) or either of the gyro sensefrequencies f₀±Ω.

In this embodiment, the reference frequency f_(R) is larger than thegyro disturbance frequencies f₀±f_(RD) and the gyro sense frequenciesf₀±Ω. The modulated frequencies of the gyro disturbance signal and thetwo gyro sense signals may be simply represented as f_(R)−(f₀.f_(RD))and f_(R)−(f₀+f_(RD)), f_(R)−(f₀.Ω) and f_(R)−(f₀+Ω), respectively.

The cut-off frequency f_(LP) of the low-pass filter 308 is controlledbetween a smaller frequency of the modulated gyro disturbancefrequencies i.e., |f_(R)−(f₀.f_(RD))| and |f_(R)−(f₀+f_(RD))|, and asmaller frequency of the modulated gyro sense frequencies, i.e.,|f_(R)−(f₀.Ω)| and |f_(R)−(f₀+Ω)|. The level of one gyro disturbancesignal is retained or amplified by the gain G_(LP), and on the opposite,the other gyro disturbance signal and the two gyro sense signals aredepressed. Upon such modulation based on mixing and low pass filtering,one gyro disturbance signal in the gyro output signal is isolated out,and the peak detector 304 may further determine whether this isolatedgyro disturbance signal exceeds the threshold level V_(TH).

One of those skilled in the art knows that the gyro sensing circuit 300is preferably applied when the gyro disturbance signals are relativelydistant from the gyro sense signals on the frequency spectrum. Thedifference between the disturbance frequency f_(RD) and the rotationfrequency Ω needs to be sufficiently large, such that the cut-offfrequency f_(LP) may be controlled to a magnitude in between of them.Therefore, the modulation method based on one demodulation unit 302 isnot applicable when the disturbance frequency f_(RD) is substantiallyclose to the sense frequency Ω in FIG. 5C. Substantial closeness of theshock frequency with another frequency is determined based on whetherthe cut-off frequency f_(LP) of the low-pass filter 308 may beengineered to differentiate the corresponding modulated frequencies. Tobe specific, in one embodiment associated with FIG. 5C, a challengeoccurs for the gyro sensing circuit 300 that is based on a singlemodulation unit 302, when the modulated gyro disturbance frequencyf_(R)−f₀−f_(RD) and the modulated gyro sense frequency f_(R)−f₀−Ω is soclose that the low-pass filter 308 may not be easily engineered todifferentiate them.

In certain embodiments, the shock signal may also co-exist with the gyrodisturbance signals, and a similar modulation method may be applied toisolate the shock signal only or isolate both the shock signal and oneof the gyro disturbance signals.

However, the modulation method based on one demodulation unit 302 isalso not applicable, when the shock frequency f_(SK) is substantiallyclose to one of the gyro disturbance frequencies f₀±f_(RD) in FIG. 5C,and when the shock signal has to be differentiated from the gyrodisturbance signals. The gyro sensing circuit 300 that is based on onedemodulation unit 302 may fail to output a correct shock flag under thiscircumstance. Although the gyro disturbance signals are acceptable bythe rotation sensing system 200 and the host, the gyro disturbancefrequency f₀+f_(RD) may be so close to the shock frequency f_(SK) thatthe gyro sensing circuit 300 regards the gyro disturbance signals as theshock signal and issues an erroneous shock flag.

In various embodiments associated with FIGS. 4A-4C and 5A-5C, thereference signal may be selected at a single reference frequency f_(R),and however, each of the other signals related to the gyro sensesignals, the gyro disturbance signals and the shock signal may beassociated with a respective frequency bandwidth. Regardless of theirbandwidths, the gyro sense signals and the shock signal are simplyrepresented around their respective central frequencies. In thesefigures, heights of corresponding arrowed lines are not presented in aproportional format to the actual magnitudes of these signals.

FIG. 6 illustrates an exemplary block diagram 600 of a gyro sensingcircuit based on a differential demodulation scheme according to variousembodiments in the invention. The gyro sensing circuit 600 includes twodemodulation units 602A and 602B that respectively demodulate the gyrooutput signals at two reference signals f_(R1) and f_(R2), compensatethe magnitudes of the gyro output signals as needed and band-limit thegyro output signals. In particular, the two reference signals aresymmetric with respect to the characteristic frequency f₀, and may thusbe represented as f₀−Δf_(R) and f₀+Δf_(R), respectively. The demodulatedgyro output signals are further combined differentially by a subtractor604. A peak detector 606 further detects whether the magnitude of thecombined output signal exceeds a threshold level V_(TH), and generates acorresponding shock flag to alert the host whether an anomalous shock ordisturbance situation occurs.

Such a differential demodulation method is applied to address the abovechallenges in the non-differential demodulation scheme, when the shockfrequency f_(SK) of the shock signal is close to any frequency of thegyro sense signals or the gyro disturbance signals. This method takesadvantages of the symmetric nature of both the gyro sense signals andthe gyro disturbance signals. These symmetric signals, once demodulatedby symmetric reference signals, may substantially cancel off each othervia differential combination in the subtractor 604. As a result, theshock signal may be detected with an enhanced immunity to vibrationalsense or disturbance signals coupled in the gyro output signal.

FIG. 7A illustrates a third exemplary spectrum diagram 720 of inputscoupled into a rotation sensing system according to various embodimentsin the invention. In addition to interested rotation of the gyroscope202, both a rotational disturbance and a shock may be incorporated intothe gyro output signal. In various embodiments, the disturbancefrequency f_(RD) of the rotational disturbance may be located within anintermediate frequency range, e.g., 1-5 kHz, while the shock frequencyf_(SK) of the shock may have a higher frequency. The characteristicfrequency f₀ of the gyroscope 202 may be located in between of thedisturbance frequency f_(RD) and the shock frequency f_(SK).

FIG. 7B illustrates an exemplary spectrum diagram 740 of signalcomponents in a gyro output signal and two reference signals used in agyro sensing circuit according to various embodiments in the invention.The interested rotation of the gyroscope 202 is coupled based on theCoriolis force, and modulated to two gyro sense signals that aresymmetric with respect to the characteristic frequency f₀. Similarly,the rotational disturbance to the gyroscope 202 is also modulated to twogyro disturbance signals that are symmetric with respect to thecharacteristic frequency f₀. These two gyro disturbance signals and thetwo gyro sense signals constitute the signal components in the gyrooutput signal provided to the rotation sensing system 200. In someembodiments, the gyro disturbance signals may be further apart from thecharacteristic frequency f₀ compared with the gyro sense signals.

In addition to the gyro sense and disturbance signals, the gyro outputsignal further comprises a shock signal that has a shock frequencyf_(SK). This shock signal is not modulated by the gyroscope 202 and isdirectly incorporated into the gyro output signal. Therefore, the shocksignal is not symmetric with respect to the characteristic frequency f₀.

In view of these signal components, two reference signals are applied todemodulate the gyro output signal in the gyro sensing circuit 600. Thefirst reference signal used by the first demodulation unit 602A has afirst reference frequency f_(R1) that is larger than the characteristicfrequency f₀ by Δf_(R), and the second reference signal used by thesecond demodulation unit 602B has a second reference frequency f_(R2)that is smaller than the characteristic frequency f₀ by Δf_(R). As aresult, the reference signals, the gyro sense signals and the gyrodisturbance signals are symmetric with respect to the characteristicfrequency f₀ except the shock signal.

The first reference frequency f_(R1) of the first reference signal isselected to be closer to the shock signal and the gyro disturbancefrequency f₀+f_(DR) than to the gyro sense frequency f₀+Ω, and thesecond reference frequency f_(R2) is therefore closer to the gyrodisturbance frequency f₀−f_(DR) than to the gyro sense frequencies f₀.Ω.The reference frequencies f_(R1) and f_(R2) need to be sufficiently farfrom the peak frequency f₁ of the gyroscope 202 due to the undesirableintrinsic vibrational mode at this peak frequency, while not being sofar that responses from the shock signal and the gyro disturbancesignals are compromised.

FIG. 7C illustrates an exemplary spectrum diagram 760 that indicates adifferential demodulation mechanism to separate the shock signal fromthe gyro sense and disturbance signals according to various embodimentsin the invention. Due to their symmetry with respect to thecharacteristic frequency f₀, the two gyro sense signals are demodulatedto two sense signals at identical frequencies Δf_(R)±Ω by both the firstand second demodulation units 602A and 602B, except that the positionsof the two demodulated sense signals are opposite in the frequencyspectrum 760 of the two corresponding demodulations. Likewise, the twogyro disturbance signals are demodulated to two disturbance signals atidentical frequencies Δf_(R)±|f_(RD)−f_(p)|, and the positions of thetwo demodulated gyro disturbance signals are also opposite in thefrequency spectrum 760 of the two corresponding demodulations. Incontrast with the gyro sense and disturbance signals, the shock signalis asymmetric with respect to the characteristic frequency f₀, and thedemodulated shock signals respectively centers at two distinctfrequencies |f₀+Δf_(R)−f_(SK)| and |f₀+Δf_(R)−f_(SK)| in the frequencyspectrum 760 associated with the two corresponding demodulations.

Although the respective two frequencies of either the demodulated senseor disturbance signals match, their amplitudes are not necessarily so,because the gyroscope 202 that has the characteristic frequency f₀ andthe peak frequency f₁ may have distinct filtering effects on the signalsthat are symmetric with respect to the characteristic frequency f₀. Inaccordance with some embodiments, the demodulated gyro output signalsare compensated within the first and second demodulation units 602A and602B in order to neutralize the filtering effects of the gyroscope 202.In one embodiment, such compensation is mainly obtained by tailoring thegains G_(LP1) and G_(LP2) for filtering in the first and seconddemodulation units 602A and 602B. In another embodiment, the phasesΦ_(R1) and Φ_(R2) of the first and second reference signals are alsoadjusted to compensate filtering effects of the gyroscope 202. Based onsuch compensation, the amplitudes of the demodulated disturbance signalsmatches with each other and may be cancelled off by subtraction, and insome embodiments, so do the amplitudes of the demodulated sense signals.

The cut-off frequencies f_(LP1) and f_(LP2) are equal for filtering inthe first and second demodulation units 602A and 602B. Due todifferential combination in the subtractor 604, the cut-off frequenciesf_(LP1) and f_(LP2) are relatively easier to control. In certainembodiments, both the demodulated disturbance signals and thedemodulated sense signals are matched, so the cut-off frequenciesf_(LP1) and f_(LP2) just need to be controlled between the distinctfrequencies |f₀+Δf_(R)−f_(SK)| and |f₀+Δf_(R)−f_(SK)| of the twomodulated shock signals. When the second demodulated gyro output signalis subtracted from the first demodulated gyro output signal, themodulated gyro disturbance signals and the modulated gyro sense signalsautomatically cancel off each other.

In one embodiment, the amplitudes of the demodulated disturbance signalsare matched, while those of the demodulated sense signals are not. Thecut-off frequencies f_(LP1) and f_(LP2) need to be better controlledbelow the frequencies of the demodulated sense signals, such that theuncompensated sense signals may be suppressed by filtering.Nevertheless, it is easier to control the cut-off frequencies f_(LP1)and f_(LP2) in such a manner than to control them between the shocksignal and the demodulated disturbance signals.

Based on two differential demodulations, one shock signal in the gyrooutput signal is isolated, and the peak detector 304 may furtherdetermine whether this isolated shock signal exceeds the threshold levelV_(TH). One of those skilled in the art knows that the gyro sensingcircuit 600 is effective to address the issues when the frequency of theshock signal is close to that of one gyro disturbance signal and/or thatof one gyro sense signal.

In various embodiments associated with FIGS. 7A-7C, the referencesignals may be selected at the two specific reference frequencies f_(R1)and f_(R2), and however, each of the other signals concerning the gyrosense signals and the shock signal may be associated with a respectivefrequency bandwidth. Regardless of their bandwidths, the gyro sensesignals and the shock signal are simply represented around theirrespective central frequency. Like FIGS. 4A-4C and 5A-5C, heights ofcorresponding arrowed lines in FIGS. 7A-7C are not presented in aproportional format to the actual magnitudes of these signals.

FIG. 8 illustrates another exemplary block diagram 800 of a gyro sensingcircuit based on a differential demodulation scheme according to variousembodiments in the invention. As an embodiment of the gyro sensingcircuit 600, either of the demodulation units 602A or 602B comprises anelectronic mixer and a low pass filter that are coupled to each other.The electronic mixers 802A and 802B in the demodulation units 602A or602B mix the gyro output signal with two reference signals that adopttwo distinct reference frequencies (f₀+Δf_(R) and f₀−Δf_(R)) and twodistinct phases (Φ_(R1) and Φ_(R2)), respectively. The correspondinglow-pass filters 804A and 804B further filter the respective mixed gyrooutput signals based on two distinct gains G_(LP1) and G_(LP2) but twoconsistent cut-off frequency f_(LP1) and f_(LP2). The two consistentcut-off frequency f_(LP1) and f_(LP2) is equal to one single frequencyf_(LP). In various embodiments of the invention, the phases Φ_(R1) andΦ_(R2) of the reference signals and/or the gains G_(LP1) and G_(LP2) ofthe filters are tailored to compensate the potentially distinctfiltering effects that the gyroscope 202 have on the gyro sense anddisturbance signals having frequencies higher or lower than thecharacteristic frequency f₀.

The two demodulated gyro output signals are differentially combinedwithin the subtractor 604, such that the second demodulated gyro outputsignal is subtracted from the first demodulated gyro output signal togenerate a combined gyro output signal. Due to compensation, the twodemodulated gyro disturbance signals cancel off each other in the twodemodulated gyro output signals, and in some embodiments, so do the twodemodulated gyro sense signals. The demodulated shock signal is includedin the combined gyro output signal and effectively isolated from thegyro sense or disturbance signals.

The following peak detector 606 comprises a sampling circuit 806 and acomparator 808. The sampling circuit 806 samples the combined gyrooutput signal received from the subtractor 604. The comparator 808compares the sampled signal with the threshold level V_(TH) andgenerates the shock flag according to a comparison result.

FIG. 9A illustrates an exemplary flow diagram 900 of a method forflagging a disturbance or a shock experienced by a rotation sensingsystem according to various embodiments in the invention. FIG. 9Billustrates another exemplary flow diagram 950 of a method for flagginga shock experienced by a rotation sensing system according to variousembodiments in the invention. The methods 900 and 950 are based on anon-differential demodulation scheme and a differential demodulationscheme, respectively.

The method 900 of flagging the shock or disturbance initializes withreceiving a gyro output signal from a gyroscope at step 902. Besidesgyro sense signals related to an interested rate of rotation, the gyrooutput signal further includes the shock signal or the gyro disturbancesignals.

In order to separate a shock signal or a gyro disturbance signal, such agyro output signal is demodulated using a reference signal that has areference frequency f_(R) at step 904. During demodulation, the gyrooutput signal is mixed with the reference signal, and further bandlimited according to a cut-off frequency f_(LP). The shock signal or thegyro disturbance signals included in the gyro output signal is thereforedemodulated together with the interested gyro sense signals. In oneembodiment, the shock signal exists while no gyro disturbance signalsare involved, so the cut-off frequency f_(LP) is set between thefrequencies of the demodulated shock signal and the demodulated gyrosense signals. In another embodiment, the gyro disturbance signals areinvolved in the gyro output signal while no shock signal isincorporated, so the cut-off frequency f_(LP) is set between therespective lower frequencies of the demodulated gyro sense anddisturbance signals. In certain embodiments, both the gyro disturbancesignals and the shock signal are included in the gyro output signal inaddition to the gyro sense signals, and the cut-off frequency f_(LP) isset between the frequency of the demodulated shock signal and the lowerfrequency of the demodulated gyro disturbance signals or between therespective lower frequencies of the demodulated gyro sense anddisturbance signals. As a result, the demodulated shock signal or onedemodulated gyro disturbance signal is retained, while the other signalcomponents are depressed in the demodulated gyro output signal.

At step 906, it is determined whether the demodulated gyro output signalexceeds a threshold value V_(TH)A shock flag is issued to a host of therotation sensing circuit to acknowledge existence of the shock ordisturbance and corruption of the gyro sense signals related to theinterested rotation information.

The method 950 of flagging the shock or disturbance also initializeswith receiving a gyro output signal from a gyroscope at step 952.Besides gyro sense signals related to an interested rate of rotation,the gyro output signal includes a shock signal, and may furtherincorporate gyro disturbance signals as well. The gyro sense anddisturbance signals are symmetric with respect to the characteristicfrequency f₀ of the gyroscope, while the shock signal is not so.

At step 954, such a gyro output signal is demodulated using a firstreference signal that has a first reference frequency f_(R1). At step956, the gyro output signal is also demodulated using a second referencesignal that has a second reference frequency f_(R2). During eitherdemodulation, the gyro output signal is mixed with the first or secondreference signal and further band limited according to a cut-offfrequency f_(LP1) or f_(LP2). The first and second reference signals areselected to be symmetric with respect to the characteristic frequencyf₀. The phases of the first and second reference signals and/or thegains of band limiting are adjusted to compensate distinct filteringimpacts the gyroscope has on distinct gyro sense signals or distinctgyro disturbance signals. The demodulated gyro sense signals haveconsistent magnitudes upon such compensation, and so do the demodulatedgyro disturbance signals if they are originally incorporated.

At step 958, the first demodulated gyro output signal from step 954 isdifferentially combined with the second demodulated gyro output signalfrom step 956. In some embodiments, the gyro sense signals that aresymmetric to the characteristic frequency f₀ are substantially cancelledoff, and so are the gyro disturbance signals if they are incorporated inthe gyro output signal. As a result, the combined gyro output signalincludes the demodulated shock signal that is therefore isolated fromthe gyro sense and/or disturbance signals.

At step 960, it is determined whether the combined gyro output signalexceeds a threshold value V_(TH). A shock flag is issued to a host ofthe rotation sensing circuit to acknowledge existence of the shock ordisturbance and corruption of the gyro sense signals related to theinterested rotation information.

The method 900 that is based on non-differential demodulation involves asingle demodulation step, but is difficult to apply when a shock signalis close to a gyro sense signal or a gyro disturbance signal. Incontrast, the method 950 involves two complementary demodulation stepsand may be applied in the above challenging situation that the method900 has difficulty to handle.

While the invention is susceptible to various modifications andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsdisclosed, but to the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the scope ofthe appended claims.

We claim:
 1. A gyro sensing circuit based on a differential demodulationscheme, comprising: a first demodulation unit, coupled to receive a gyrooutput signal from a gyroscope, the first demodulation unit demodulatingthe gyro output signal to a first demodulated gyro output using a firstreference signal, the gyro output signal comprising a shock signal and aplurality of gyro sense signals that are related to an interested rateof rotation; a second demodulation unit, coupled to receive the gyrooutput signal, the second demodulation unit demodulating the gyro outputsignal to a second demodulated gyro output using a second referencesignal, the first and second reference signals being symmetric withrespect to a characteristic frequency of the gyroscope; a subtractor,coupled to the first and second demodulation units, the subtractordifferentially combining the first and second demodulated gyro outputsto isolate the shock signal that is asymmetric with respect to thecharacteristic frequency; and a peak detector, coupled to thesubtractor, the peak detector determining whether the combined gyrooutput exceeds a threshold level and generating a shock flag to alert ahost whether an anomalous shock or disturbance situation occurs.